What Causes the Abnormal Noise When an Automatic Transmission Car Starts at Low Speed?
4 Answers
"The causes of abnormal noise when an automatic transmission car starts at low speed include: engine failure, transmission failure, and door wear. Below is a detailed explanation of the above causes: Engine failure: Abnormal noise from the engine indicates a problem in the engine compartment, such as a metallic screeching or whistling sound, mainly caused by excessive wear of some parts or improper assembly and adjustment. Therefore, when the engine makes abnormal noises, it should be repaired promptly to prevent the fault from worsening. Transmission failure: If there is a "rustling" sound inside the transmission while driving, which disappears when the clutch or accelerator pedal is pressed, and a whistling-like sound occurs during gear shifting, the transmission should be repaired immediately. Door wear: When stepping on the accelerator or brake, there might be some abnormal noises from certain parts of the car body, mainly due to lack of lubrication in the door. However, it is necessary to determine whether the noise comes from the door hinge position or the internal components of the door, such as the window regulator, door lock mechanism, or handle mechanism. If the noise is from the door hinge or limiter, a specialized door hinge and slide lubricant can be used. For the internal components like the window regulator, door lock mechanism, or handle mechanism, a specialized door accessory lubricant should be used."
I've been driving an automatic transmission car for several years and have also experienced that clunking sound during low-speed starts. The most likely cause is the brake discs and pads not fully separating, especially right after washing the car or during rainy days when the discs are prone to rust - the grinding noise occurs when starting off. Another possibility is issues with the CV joint (constant velocity joint); if you hear clicking noises during acceleration while turning, you should be more alert. A torn boot on the drive shaft causing insufficient lubrication is also a common reason - just bend down and check if there are any oil stains under the chassis. Last time my car made such noises, the shop found it was caused by aged engine mount bushings creating resonance noise, and replacing them for 300 yuan fixed it. These minor issues can turn into major problems if not addressed promptly.
Once when I was dropping my child off at school, I heard a creaking sound from under the car as I slowly started in the garage, which scared me into getting it checked immediately. The mechanic said it was an issue with the suspension system, such as aging stabilizer bar bushings or wear on the lower control arm ball joints. These rubber components can crack over time and make friction noises when the car moves. Additionally, if the transmission mount is loose, the engine can wobble and produce a thumping sound during acceleration. I've also experienced loose exhaust pipe mounting bolts before, which caused metallic knocking sounds at low speeds due to vibrations. When encountering these issues, don't try to dismantle anything yourself—recording the type of abnormal noise with your phone and playing it for the mechanic can save a lot of trouble. Now, during every maintenance check, I make sure the mechanic pays special attention to the condition of the chassis rubber components.
If your car makes a whining or rustling noise during low-speed starts, there's an 80% chance it's a transmission issue. With over a decade of experience studying cars, I've found three common scenarios for automatic transmissions: the transmission fluid needs replacing, as thickened fluid affects clutch plate engagement; worn torque converter lock-up clutch plates can produce a rustling sound; and unstable valve body oil pressure can cause jerky shifting. Also, don’t overlook wheel bearing issues—aged bearings often produce a humming noise during low-speed turns. For diagnosis, lift the car, shift to D, and let the wheels spin freely to listen for the clearest sound. I recommend following the maintenance manual to change transmission fluid regularly, which can prevent most abnormal noises.
